Satellite based positioning systems include networks of earth orbiting satellites that constantly transmit geographical position information to receivers. An example of a satellite based positioning system is the Global Positioning System (GPS), which includes a network of earth orbiting satellites (GPS satellites or satellite vehicles). A GPS receiver can be in a fixed position on a base station or location server, or the receiver can be on a mobile unit or station. The GPS receiver and known processing hardware and software are used to receive GPS data from GPS satellites and determine the position of the receiver. GPS technology was first used in military and emergency service applications. As GPS technology becomes more economical and compact, however, it is becoming ever more common in consumer applications. For example, many location based services (LBS) now exist, such as asset tracking, turn-by-turn routing, and friend finding.
The wireless community is investigating procedures and methodologies for LBS that most benefit both the consumer and the provider. The change in focus from emergency to commercial services is characterized by an increased number of users, an increased number of positioning requests per user, and an increase in the accuracy needed to meet various LBS quality of service requirements. As the demand for LBS capabilities grows, the number of users taking advantage of those services will potentially outstrip those transmitting requests for emergency services. Additionally, a number of these services (turn-by-turn routing, for example) involve each user requiring repeated location solutions, which is in contrast to the single position request that characterizes an emergency call. Finally, many of the LBS that are being planned require accuracies far greater than those required for regulatory compliance.
The diversity inherent in proposed LBS offerings presents LBS providers with many choices and challenges. For example, some LBS work better with a mobile station (MS) based approach while others are better served by an MS-assisted solution.
It is desirable to have a satellite based positioning method and system that is able to handle greatly increased LBS system usage while allowing a system operator the flexibility to choose between MS based, MS-assisted, or other approaches. It is further desirable to have a satellite based positioning method and system with the high accuracy required by most LBS. It is desirable to have a satellite based positioning method and system that minimizes the use of network resources while also minimizing the power used by mobile stations.